The compound 2-methyl-4-(4-methyl-1-piperazinyl)-10H-thieno[2,3-b][1,5]benzodiazepine compound has useful central nervous system activity. Certain tablet formulations of olanzapine are known, as described in U.S. Pat. No. 5,229,382. However, improved oral formulations were desired in light of the moisture sensitive, polymorphic nature of olanzapine, the tendency of olanzapine to undesirably discolor in the known tablet formulation, and due to the surprisingly potent nature of olanzapine.